(a) Technical Field of Invention
This invention relates to an electroconductive coating composition and, in particular, to an antistatic article comprising a polymeric substrate having, on at least one surface thereof, a layer of the electroconductive coating composition.
By an "antistatic article" is meant a treated polymeric article exhibiting a reduced tendency, relative to an untreated article, to accumulate static electricity on a surface thereof.
Articles in accordance with the invention may be produced by conventional polymer-forming techniques, including moulding, blowing, casting and extrusion, and may comprise fibres, filaments, sheets, films and the like, and particularly photographic films. For ease of discussion the invention is hereinafter described with reference to films.
(b) Background of the Art
The tendency of polymeric articles, such as films, to accumulate detrimental static electrical charges on surfaces thereof is well known. The presence of such charges creates a variety of problems including the attraction of dust and other contaminants to the film surface, the creation of a potential explosion hazard in the presence of organic solvents, difficulties in feeding the films through film handling and treating equipment, blocking, ie adhesion of the film to itself or to other films, and the risk of fogging subsequently applied light-sensitive coating layers. Consequently, it has been proposed to improve the electrical surface conductivity of polymeric films by treating the film with one or more of a variety of antistatic agents, the selected antistatic agent either being applied directly to a surface of the film, suitably in a volatile coating medium, or being incorporated into the polymeric material prior to fabrication of a film therefrom in the expectation that the antistatic agent will eventually migrate to a surface of the film.
Although many antistatic agents and coating compositions have been proposed for use in the treatment of film surfaces, their use is generally subject to a variety of constraints. For example, many available antistatic coating compositions are relatively hydroscopic, becoming swollen or softened by contact with moisture and therefore lack permanence when applied to substrates which may subsequently be exposed to relatively high degrees of humidity. In particular, water-soluble antistatic compositions are prone to removal during conventional photographic aqueous-processing techniques, and therefore are less than satisfactory in the treatment of photographic products, such as microfilms. Thus, a microfilm fiche or reel from which an applied antistatic coating medium has been partially removed during processing may be susceptible to pick-up of dust with consequent deleterious effects on the product. Such defective products also exhibit a blocking phenomenon whereby adjacent layers of microfilm tend to stick to each other to the detriment of the handling characteristics of the product. Furthermore, water-soluble antistatic coatings tend to be relatively soft, and therefore liable to abrasion during subsequent processing and handling-with the attendant generation of unacceptable debris, usually referred to as "pay-off" in the photographic art. Abrasion of an antistatic backing layer is of particular concern in relation to reeled films intended for use in high speed document-copying cameras. Backing "pay-off" is also particularly serious when it occurs during subsequent deposition, on the opposite surface of the film, of additional layers--such as anti-halation and light-sensitive photographic emulsion layers. Transfer of abraded debris from the antistatic backing layer into the opposed emulsion layer may result in the generation of unacceptable pin-holes in the finished product.
We have now devised an electroconductive coating composition which eliminates or substantially overcomes the aforementioned difficulties.